I cant tell why its hapening, maybe because its to heavy?
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Ok cool, I figured it had something to do with mass @AndrewGarrison
I spent some time today looking into this. There are some issues with the wheels, but the majority of this problem is solved by increasing the mass of the wheels.
I just tried reverting everything from massScale="0" to "1" and it still is bouncing around. Thanks for the bug report. We'll look into it.
I noticed you are using a lot of massScale="0", which can cause some instability in crafts as it is inherently non-physical. Do you notice issues if massScale is not zeroed out?